Boat in water over winter....heater needed?

parsifal said:
Plenty of ventilation is all that's needed.
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I agree. My boat has always wintered afloat, and I was plagued with damp and mildew, even when using loads of chemical dehumidifiers. The boat is an Achilles 24 and has one mushroom vent in the coachroof as standard. Then about 7 years ago I added 2 more ventilators, a teak louvre in the companionway hatch, and a mushroom vent retro-fitted to the forehatch. The result is a complete turn-around from damp and mildew to dry as a bone. An amazing result - far better than I had hoped.
 
Gladys said:
As far as dehumidifiers are concerned, the main thing is to have one on a time switch, so that it DOESN'T run overnight, when freezing is more likely. MIne runs from about 0930-1630. Works well for me...
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That depends on the type of dehumidifier - bad idea to cut off a desiccant dehumidifier like the very popular Meaco one in mid cycle. See separate threads on this - including high tech solutions to switching off when not operating
 
Minn said:
I have always tried to ensure a howling draft through the boat, all year round, and this seems to work well.

If you are on board in the winter and warm things up, restricting the howling draft, you open things up again as you leave.
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Unless you don't leave...
 
Dehumidifier is the way forward. The difference between a well ventilated boat and one with a dehumidifier is the way the ventilated boat owner opens the boat and says, "See no smell", while a horrible whiff knocks out the person behind them. With a dehumidifier there really is no smell and it does slightly heat the boat as well. The timer idea makes no sense at all as the coldest part of the 24 hour cycle is exactly when the moisture is released and you most want the slight heating.

Maeco Junior is the PBO recommended one and uses little power once the boat is dry is very reliable (4 years on ours is still going fine left for 3-5 months completely unattended every year) and most importantly starts itself up at the last settings without human intervention after a power loss (marina rebooting, somebody borrowing your socket for a few days).
 
Gladys said:
As far as dehumidifiers are concerned, the main thing is to have one on a time switch, so that it DOESN'T run overnight, when freezing is more likely. MIne runs from about 0930-1630. Works well for me...
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It's compressor type dehumidifiers that freeze (and work very poorly at low temperatures). Freezing can block the fan turning, and then cause motor to burn out.

Electric dessicant types work just as well at low temperatures as at high, though use a bit more power. Meaco DD8L Junior is the usual choice these days.
 
I have a cheapo compressor type in my garage. If it gets too cold, it switches off and the 'defrost' light comes on.
When it's that cold you don't really need a dehumidifier.
To get things dry, running it in the warmer part of the day seems most efficient.
 
lw395 said:
I have a cheapo compressor type in my garage. If it gets too cold, it switches off and the 'defrost' light comes on.
When it's that cold you don't really need a dehumidifier.
To get things dry, running it in the warmer part of the day seems most efficient.
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It's the opposite - more water comes out of the air at lower temperatures so that's when you want the dehumidifier running to slightly warm the air and minimise the dew every night inside. In practice though after the first week of the boat being sealed up there shouldn't be much moisture left.
 
RupertW said:
It's the opposite - more water comes out of the air at lower temperatures so that's when you want the dehumidifier running to slightly warm the air and minimise the dew every night inside. In practice though after the first week of the boat being sealed up there shouldn't be much moisture left.
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The air 'holds more water' the warmer it is.
So the dehumidifier extracts more water from the air when it's warmer.
In general the problem is not actually water vapour in the air, it's water contained in fabrics, wood etc, or lying in odd corners of the bilge. The aim of the game is to remove this water, which is done much quicker when it's warm.
If you can get the relative humidity down to about 20% in the afternoon, you generally don't get significant condensation overnight.

And mold etc doens't grow when it's fridge cold anyway.

If you have rain leaks and permanent bilge water and never get the boat dry, this approach won't work.

I have tried running my dehumidifier at various times with a watthour meter and a min-max thermometer/hygrometer. I'm fairly serious about it because I have some expensive stuff in the garage.
There are other things going on, like the boat/garage will be warmer than the outdoor air at night, so any air which leaks in can only have a limited absolute water content, which translates to not enough humidity to condense in the garage. Whereas in the morning, the air outside can be warmer and humid.

At night, when it's pretty cold, say below 10degC in the garage, a small heater is effective at keeping the humidity down, provided you are only dealing with water vapour which comes in from air leaks. Of course the humidifier is putting out some watts of waste heat when it's working so it still helps.
 
Try to check every so often; I have known boats have flooded cockpits - and I suppose may eventually have sunk - when snow and fresh water rain became ice and blocked the drains - same goes for leaves if she's near or under trees ( unlikely at Port Solent I know but thought I'd mention it ).
 
maby said:
A great deal depends on whether or not you use the boat over the winter and what the weather was like when you closed it up if you are not going to use it. We spend several days on the boat every week, all the year round, and it would be a disaster without a dehumidifier. You spend two or three days aboard, cooking, eating, living with the heating on and the amount of water in the air builds up - but the humidity stays down because the air is being heated. You then turn off the heating and leave the boat - which cools rapidly - and the humidity rockets. We don't usually leave the dehumidifier running while we are away, but it is on most of the time we are aboard, so we leave a warm boat full of dry air - which translates to a cold boat full of relatively dry air. I'm just looking back on the logs from our boat - when we left it the temperature was around 20 degrees and the humidity was about 45%. At the moment, the temperature is 5 degrees and the humidity is 60%
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When you are on the boat using heating, cooking and just breathing, the air becomes very humid. The humidity remains in the warm air and when the surfaces within the boat cool, water vapour condenses on them. Cold air is much dryer than warm air (see "Meteorology"). It would be a better idea to open all hatches and let the boat air well before leaving, allowing your dehumidifier to have a much lighter workload.
My own preference is to forget about dehumidifying and leave the fore-hatch on the 'ventilation' setting, allowing the air to flow in through the louvres in the washboards. I have done this every winter since buying the boat with no recurrence of the black mould that was on every surface after the previous owners had left it completely sealed up over winter.
 
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